The present invention relates to a method and apparatus for making single cranks which are used to build-up crankshafts for large engines.
Crankshafts for ships' engines and other large engines are made from a plurality of single cranks and shaft sections. The cranks and shaft sections are assembled together to form a crankshaft. The number and size of cranks used in the built-up crankshaft is dependent upon the horsepower of the engine. Ships' engines may have an output of up to 50,000 horsepower. The cranks used in building-up crankshafts for these engines must also be very large. For example, each crank for a large engine crankshaft may weigh approximately 20 tons. The crank may be about 72-inches long and have a width of 54-inches and a crank arm thickness of 17.5-inches. Manufacture of such large cranks is difficult and in the past has required special equipment as well as considerable machining to obtain the finished shape and size.
A special rotary-hinge type apparatus is shown in Russian Pat. No. 323,183 for making large single cranks. A method using a similar apparatus is described in Japanese Examined Patent Application No. J76-93764. The cranks made on such apparatus are rough-shaped forgings and require considerable complex machining on large equipment due to the fact that most of the machining must be performewd on the final-shaped forging configuration.
It is therefore a primary object of the invention to provide a method of making more precise large single cranks on a conventional open-die press.
It is another object of the invention to provide a method for making large single cranks with significantly reduced final machining.
It is still another object of the invention to provide apparatus for forging very long horizontally elongated workpieces in a semi-closed die assembly on a conventional open-die press.